1. Field of the Invention
This invention relates to an optical fiber communication method and a transmitting device, more particularly to an optical fiber communication method and a transmitting device using a second-order fiber Bragg grating structure.
2. Description of the Related Art
A fiber Bragg grating (FBG) is a type of Bragg grating formed in a core of an optical fiber, and is achieved on account of a periodically varying refractive index of the core. A first-order Bragg grating has a wavelength selection property, i.e., it reflects light in a narrow band around a Bragg wavelength and transmits light in all others. The Bragg wavelength is expressed in Equation 1 that follows:λB=2neff·Λ  (Equation 1)where λB represents the Bragg wavelength, neff represents an effective refractive index defined by the periodically varying refractive index of the first-order Bragg grating, and Λ represents a period of variation of the periodically varying refractive index of the first-order Bragg grating.
A second-order Bragg grating has the aforesaid wavelength selection property, and further has a surface radiation property, i.e., it radiates light in a narrow band around a particular wavelength. The particular wavelength is expressed in Equation 2 that follows:λ≈λB=neff·Λ  (Equation 2)where λ represents the particular wavelength, λB represents the Bragg wavelength, neff represents an effective refractive index defined by the periodically varying refractive index of the second-order Bragg grating, and Λ represents a period of variation of the periodically varying refractive index of the second-order Bragg grating.
It is disclosed in U.S. Pat. No. 6,766,078 that the second-order Bragg grating can be applied in free space couplers, optical sensors, and suppression of ripples in dispersion compensators, etc.